Additional Student t Distribution Functions in Excel

  Excel has two additional functions related to the cumulative Student t distribution for use in hypothesis testing, T.DIST.RT and T.DIST.2T. The values in the table below are calculated two ways, one using an Excel function and the second using the cumulative t distribution. The function T.DIST.RT computes values of the single tailed probability, p(t̃<t), that is, the probability that Student's t will be greater than t̃ which is seen to be equal to the probability that t is not less than t̃ which can be computed using the cumulative distribution.The two tailed function T.DIST.2T gives the probability
p(not -t̃<t<t̃) or the probability that t is not in the interval bounded by -t̃ and t̃. Note that this function is only defined for 0<t̃. Note that if B=not A then p(B)=1-p(A) since the probability of both p(A)+p(B)=1.

As t̃ increases the probabilities decrease since the area under the curve for the t probability density function decreases.

The following plots help to visualize the probabilities associated with one tail and two tails.